1. Field of the Invention
The present invention relates to an apparatus for measuring the deflection angle of the optical axis of a light beam projected from an automotive headlight.
2. Description of the Prior Art
When a car is driving at night or in a similar condition, its headlights should not dazzle the driver of a car driving in the opposite lane or people walking toward the car but provide sufficient illumination for the driver to have an easy viewing in front of the car. For these purposes, it is legally prescribed that the angles of the optical-axis deflection (deviation) of the light beam projected from the headlight in the horizontal and vertical directions should be within the respective predetermined allowable ranges.
Accordingly, for example, after manufacture and assembling of a car or during inspection after the car has been used for a predetermined period, the optical-axis of the headlight is measured to check whether its angle of deflection is within the predetermined allowable range. For such measurement of the optical-axis deflection angle of the headlight, a variety of measuring apparatuses have been proposed so far.
One of the well-known apparatuses for measuring the optical-axis deflection angle of light beam projected from an automotive headlight will be described by way of example with reference to FIG. 1. FIG. 1 illustrates that a car 100 is stopped at a predetermined position while an optical-axis deflection angle measuring apparatus 102 is spaced at a predetermined distance L from a headlight 101 of the car 100. As will be seen from FIG. 2, the optical-axis deflection angle measuring apparatus (will be referred to as "measuring apparatus" hereinbelow) 102 comprises a base 103 and a screen 104 freely movable vertically (in the Y-direction) and horizontally (in the X-direction). The light projected from the headlight 101 is collected in the main unit 106 through a converging lens 105, and projected onto the screen 104. For measurement of the optical axis of the light with the measuring apparatus 102, the screen 104 is positioned in the vertical and horizontal directions, the position of the optical axis of the light projected on the screen 104 is determined while viewing through the view-finders 107 and 108, and then the deflection angle of the optical axis is calculated from the measured position thereof.
With such measuring apparatus, however, the inspecting worker positions the screen with respect to the headlight in a manual and visual manner using the finders. Thus, much labor and time are needed for attaining a positioning of the screen in a precisely aligned relationship with the headlight, and such positioning is possible inaccurate in some cases.
Also with such measuring apparatus, the inspecting worker visually locates the optical axis from the light projected on the screen for determination of the position of the optical axis. This work requires the worker to have a sharp sense, a high skill and much experience. That is, the work is difficult and thus likely to be erroneous.